Bag closure



Jan. 9, 1958 A FRlEDMAN 3,362,302

BAG CLOSURE Filed Aug. l2, 1965 F/af.

IN VEN TOR. 45e/www /e/.f @M4/M United States Patent Office 3,362,302Patented Jan." 9, 1968 3,362,302 BAG CLOSURE Abraham Friedman, Brooklyn,N.Y., assigner to Studley Paper Company, Inc., a corporation of New YorkFiled Aug. 12, 1965, Ser. No. 479,148 12 Claims. (Cl. 93-35) Thisinvention relates to manufacture of paper and plastic bags and the like.In particular, this application relates to methods of closing an end ofa tubular structure of sheet material to lform a bag thereof.

In the usual methods for manufacture, su-ch as grocery bags, shoppingbags, vacuum-cleaner filter bags and the like, as well as envelopes andthe like, it is common practice to prepare a tubular member of sheetmaterial, for example by folding the side edges of a flat blank inwardlyand gluing them together, and then close an end of the resulting iiattubular structure in any of a variety of Ways. The most common methodsof closing the end have involved folding an end one or more times toprovide a hem-like closure, and either gluing or stitching, or both, tohold the end of the bag in the resulting folded and closedconfiguration. Conventional grocery bags are folded in a somewhatdilferent manner, to provide the feature of exhibiting a fiatrectangular bottom when the bag is opened up for use, but are also madein much the same manner, i.e., by a combination of folding and gluing.

Although satisfactory and highly successful for many purposes, themethods of closing bag ends which involve folding and gluing are subjectto certain disadvantages. For one thing, the machinery required forproducing the folded configuration is complicated and expensive.Moreover, where a leakproof closure is required, it is diicult toachieve by such methods, because of diiiiculties encountered in theprecise control of the amount of glue applied and its flowcharacteristcis. If the amount of glue applied is relatively small,there is danger that some points along the glued surface will be devoidof glue and hence constitute leakage points. On the other hand, if thisdanger is to be avoided, it is necessary to apply an excess of glue,which tends to smear outside the glued surfaces, fouling the apparatusand causing sticking together of stacked bags, etc.

When a bag is stitched, rather than being glued, these diiiiculties arenot encountered. However, stitching is more expensive than gluing, andproduces a multiplicity of perforations in the bag material. To avoidleakage through these perforations, it is generally necessary to providea double or triple fold in the end, rather than a single fold, and thisis wasteful of material.

In the case of bags madefrom plastic materials such as polyethylenefilm, for example, the characteristics of the sheet materials used haveled to the development of certain other techniques for manufacture ofbags. One such technique is to fold a continuous flat sheet of materialin half, thus forming a U-shaped web, and to heatseal the two layers ofmaterial thus formed at intervals by a double line` of heat-sealingrunning transversely of the long axis of the web. The web issubsequently cut apart by transverse cuts running between each pair ofheatsealed lines, resulting in the formation of a series of bags, eachof which is closed at the bottom by the U-shaped configuration of thematerial of the web, and at the sides by a heat-sealed seam. In avariation of this method, a web of plastic material is bent to a U-fold,as just described,` and the open' side of the web is heat-sealed to forma dat, tubular structure. Alternatively, a pair of webs are laid oneatop the other, and heat-sealed along both edges, again forming a at,tubular structure. In either event, the tubular web is then heat-sealedtransversely at intervals along its length, and also perforated bytransverse perforations adjacent each transverse heatsealed region, sothat when the web is torn at the line of perforations, the torn-offportion is a bag, heat-sealed at the bottom and along one lor bothsides, and open at the top line corresponding to the line ofperforations. Such heat-sealed plastic bags have found wide usage in avariety of applications, for example as garment bags for drycleanedarticles, packagings for dry goods offered for sale, etc. However, theyare suitable only for inherently heatscalable materials such as films ofthermoplastic materials and the like. Such materials are unsuitable formany applications, in which the physical characteristics of plasticfilms are unsatisfactory `for the use for which the bag is intended.Also, even where plastic films are suitable as the construction materialfor the body of the` bag, the heatsealing method is frequentlyunsuitable because it is dilii-V cult in this manner to achieve astrong, continuous, leakproof closure without either bringing `about'adeterioration in the physical characteristics of that portion of the webwhich is actually heat-sealed, or a degradation in the properties ofadjacent portions of the web.

An object of this invention, therefore, is to provide improved methodsand apparatus for closing the ends of bags.

Another object is to provide bag-closing methods and apparatus whicheliminate the necessity for folding portions of the material of the bag.

Still another object is to as aforesaid, which do not necessitate thecontrol of application rates and iiowcharacteristics of a glue to effectclosure of the bag.

Yet another object is to for closing the ends of bags, which do notinvolve stitching the end of the bag.

A further object is to provide methods and apparatus for closing theends of bags, which are not essentially limited to use with anyparticular class of bag-construction materials. n

A still further object is to provide methods and apparatus for closingthe ends of bags, which do not result iu degradation of the propertiesof the sealed portion or adjacent portions of the bag material.

A feature of the invention is the provision of a mold adapted to form aplastic bead over the end of a bag to be closed. Another feature residesin the deposition of a 4bead of plastic over and around the adjacentedges constituting the end of a bag to be closed.

Other objects, features and advantages will become ap-` parent from thefollowing more complete description and claims, and by reference to theaccompanying drawings.

In one particularly desirable embodiment, this invention contemplates amethod of closing an end of a fiat tube of sheet material to form a bagthereof, said method comprising in combination the steps of molding abead of thermoplastic material about a pair of juxtaposed edges of anend of said fiat tube, said bead extending at least from one side to theother side of said flat tube, and hardening said thermoplastic material.

In another particularly desirable embodiment, this inventioncontemplates an apparatus for closing an end of a fiat tube of sheetmaterial to form a bag thereof, said apparatus comprising in combinationa mold having a mold cavity therein, said mold cavity having across-sectional shape corresponding to the cross-sectional shape of abead of plastic adapted to surround and seal together a pair ofjuxtaposed edges of one end of said flat tube, a passage communicatingbetween said mold cavity and the atmosphere, said passage being of asize and shape to snugly receive a double thickness of the material ofthe walls of said fiat tube adjacent an end thereof, and

means for supplying molten thermoplastic material to the interior ofsaid mold cavity.

provide methods and apparatus provide methods and apparatus Althoughadapted to the manufacture of bags of a wide variety of types,construction materials, and intended uses, this inventionis particularlyadapted to the manufacture of dust-receiving filter bags for vacuumcleaners, and will be described at least in part, with particularrespect thereto.

Referring now to the figures:

FIGURE l is a medial cross-section of one embodiment of the inventiontogether with the end portion of a bag to be sealed, just prior to thesealing operation;

FIGURE 2 is a medial cross-section similar to FIG- URE 1 but on asomewhat larger scale, showing the apparatus of the invention in theprocess of sealing the end of a bag;

FIGURE 3 is a medial cross-section of the end portion of a bag aftersealing by the process of this invention;

FIGURE 4 is a perspective View of one type of sealed bag, which may beproduced according to the invention;

FIGURE 5 is a medial cross-section similar to FIG- URE 2, depicting theoperation of an apparatus according to another embodiment of theinvention adapted to provide the upper or open end of a bag with astilfening rib and/or a carrying handle;

FIGURE 6 is a transverse cross-section taken along line `6 6 of FIGURE5;

FIGURE 7 is a perspective view of a finished bag provided with a bottomclosure and a top rib, both produced according to the presentrinvention;and

FIGURE 8 is a cross-section similar to FIGURE 5, showing a modifiedembodiment of the invention adapted t to provide the upper, open end ofa bag with a carrying handle and a stiffening rib along the inside topmargin of the bag.

Referring now more particularly to FIGURE l, the apparatus comprises amold It), which is preferably made in two mating halves, 12 and 12. Eachof the mating halves defines one-half of an internal mold cavity, thecavity halves being respectively designated 14 and 14. Communicatingwith the cavity halves are passageway halves 16 and 16 which, when themold is in closed position, define between them a passageway justsufficiently wide to accommodate a pair of juxtaposed end portions 18 ofa bag to be closed.

Also communicating with the mold cavity halves are a pair of sprues 2li,serving to feed molten thermoplastic material into the mold cavity fromappropriate external supplies thereof 22.

In the operation of this embodiment of the invention, the bag end to beclosed is inserted between mold halves `12, 12 and the latter arebrought together as illustrated in FIGURE 2. Molten plastic is theninjected from plastic supplies 22 through sprues 20 into the moldcavity, forming a bead of plastic around the juxtaposed edges of the bagend. The mold may then be left in place until the plastic solidifies andreopened, as shown in FIG- URE l, and the sealed bag end Withdrawn, orthe process may be continuous, by providing a continuous connected trainof bag ends which are continuously withdrawn in a directionperpendicular to the plane of the paper, as molten thermoplasticmaterial is continuously fed into the cavity through sprues 2t?. Ineither case, the bag end closure, in cross-section, is as illustrated inFIG- URE 3, with a solidified bead of thermoplastic material 24completely surrounding and sealing the end of the bag.

FIGURE 4 illustrates a bag made in this manner. The bag of FIGURE 4 ismade as first described above, i.e. by closing the mold over the bagend, injecting the plastic material, allowing the same to solidify, andthen opening the mold. The extrusion-type process described above wouldproduce a similar bag, except that instead of the sidewall pleats 26,there would be merely a straight heatsealed seam resulting from thetransverse heat-sealing at intervals of a continuous double web of bagwall material.

FIGURES 5-7 illustrate another embodiment of the invention which may beused to apply a stilfening top rib and/or a carrying handle or the liketo the upper, open end of a bag.

In .this embodiment of the invention, it is desired not to close the endof the bag by sealing the juxtaposed edges together, but rather to forma separate rib on each of the two edges, while leaving them separate andunconnected (except at their respective ends). Also, in the illustratedembodiment, the mold cavity is shaped to provide simultaneously a ribalong each top margin of the bag, and a carrying handle integral withthe rib.

To provide the necessary separation between the bag ends and preventtheir beingfused together, there is provided a spacing member 28 in theform of a blade of f sheet metal or the like. If the top rib is formedbefore the bottom of the bag is closed, spacing member 28 mayconveniently be inserted through the bottom of the bag and extend allthe way through the bag from below the bottom to a position even withthe top edges. Otherwise, it may be as shown, a short piece, separatelyinserted for each molding cycle, extending from the top edges a shortdistance into the interior of the bag.

The stiffening rib 30, which runs entirely around the upper edges of thebag, is formed by thermoplastic material supplied to the mold cavitythrough sprues 32 (FIG- URE 5). Thermoplastic material for the formationof handles 34, which are integral with rib 30, may be supplied throughthe same sprues, but is preferably provided for separately by way ofsprues 36.

, At the sides of the flat tube 38 forming the body of the bag, thespacer 28 extends to the inside of the fiat tube, and the mold cavityextends slightly beyond the corner of tube 3S, so as to provide for theformation of a connecting portion 40 of rib 30, which goes around theside of the bag and unites the two major portions of rib 3G on the twoat sides of the tube.

It will 'be appreciated that the embodiment of the apparatus and themode of operation described in connection with FIGURES 5-7 areessentially an injection-molding operation, and cannot readily beconverted to an extrusion type of operation, as described in connectionwith FIGURES 1-3, owing to the necessity of maintaining a separationbetween the opposed edges of the top of the bag, while at the same timeproviding for the formation of portion 4t) of the rib, encircling theside corners of the top.

The mold assembly shown in FIGURE 8 may be used to form a stilfening riband carrying handle similar to those shown in FIGURE 7, except that therib is inside the top edge of the bag instead of outside. As shown inFIGURE 8, spacer 28a is shaped to form a portion of the mold cavity, andalso grooved as at 40 to form feed channels communicating with sprues20. As molten thermoplastic material is injected through sprues 20, itsiiows in both directions through feed channels 40 to form stilfening rib30a and handles 34. Alternatively, an internal rib may be produced bythe expedient of using the apparatus as shown in FIGURES 5 and 6, andsubsequently turning the bag inside-out. This, however, involves anextra handling step which is not required when the rib is produced usingthe apparatus shown in FIGURE 8. Moreover, it would necessitate areversal of the sharp bends in the rib at the side corners of the bag,which is usually precluded by the stiffness of the molded plastic.

The apparatus and method of this invention provide an improved solutionto the problem of closing and sealing an end of a tubular body of sheetmaterial to form a bag thereof. It eliminates the need for complicatedand expensive folding apparatus, and avoids the disadvantages heretoforeexperienced from the use of. glued or stitched closures. The method ofthis invention is simple, inexpensive, and easily carried out withoutdemanding unusual skill on the part of the operator. The apparatus ofthe invention is simple and inexpensive in construction,`

virtually maintenance-free, and is readily operated, even by relativelyunskilled personnel.

While this invention has been described in terms of certain preferredembodiments and illustrated by way of certain drawings, these areillustrative only, as many alternatives and equivalents will readilyoccur to those skilled in the art, without departing from the spirit orproper scope of the invention. The invention is therefore not to beconstrued as limited, except as set forth in the appended claims.

I claim:

1. A method of closing an end of a at tube of sheet material to form abag thereof, said method comprising in combination the steps of moldinga bead of thermoplastic material about a pair of juxtaposed edges of anend of said flat tube, said bead extending at least from one side to theother side of said iiat tube, and hardening said thermoplastic material.

2. A method according to claim 1, wherein said molding is accomplishedby clamping said juxtaposed edges between mold portions, said moldportions defining a cavity surrounding said juxtaposed edges, injectinga molten thermoplastic material into said mold cavity, and hardeningsaid molten thermoplastic material.

3. A method according to claim 1, wherein said molding is accomplishedby drawing said juxtaposed edges longitudinally through a molding zone,providing a supply of molten thermosplastic material in said moldingzone, longitudinally withdrawing said juxtaposed edges together withmolten thermoplastic material from said molding Zone, and hardening saidthermoplastic material.

4. A method of forming a stilening rib on the end of a flat tube ofsheet material, comprising in combination the steps of separatingopposed edges of said end of said tube by a spacer inserted between saidopposed edges, containing said edges with said spacer in an enclosedmolding zone, surrounding said edges with molten thermoplastic material,hardening said thermoplastic material, removing said edges and saidspacer from said molding zone, and removing said spacer from betweensaid edges.

5. A method according to claim 4, wherein said spacer is positioned toproject beyond said opposed edges, and said molten thermoplasticmaterial is supplied to said molding zone in amount to form on eitherside of said spacer a pair of opposed carrying handles integral withsaid rib and projecting beyond said opposed edges.

6. A method according to claim 4, wherein said molten thermoplasticmaterial is applied to the outer margins of said opposed edges, therebyforming an external stilening rib on said edges.

7. A method according to claim 4, wherein said molten thermoplasticmaterial is applied to the inner margins of said opposed edges, therebyforming an internal stiiening rib on said edges.

8. Apparatus for closing an end of a flat tu-be of sheet material toform a bag thereof, said apparatus comprising in combination a moldhaving a mold cavity therein, said mold cavity having a cross-sectionalshape corresponding to the cross-sectional shape of a bead of plasticadapted to surround and seal together a pair of juxtaposed edges of oneend of said at tube, a passage communicating between said mold cavityand the atmosphere, said passage being of a size and shape to snuglyreceive a double thickness of the material of the walls of said flattube adjacent an end thereof, and means for supplying moltenthermoplastic material to the interior of said mold cavity.

9. Apparatus for forming a stiiening rib on the end of a flat tube ofsheet material, said apparatus comprising in combination separator meansfor maintaining a separation between said opposed edges, injection meansfor supplying molten thermoplastic material to said edges, and moldmeans for shaping said molten thermoplastic material to theconfiguration of a rib generally coinciding with said edges.

1). Apparatus according to claim 9, wherein said mold means is shaped toprovide `a pair of opposed carrying handles integral with said rib andprojecting beyond said opposed edges.

11. Apparatus according to claim 9, wherein said means for supplyingmolten thermoplastic material comprises a conduit communicating betweena supply of molten thermoplastic material and the external faces of saidopposed edges.

12. Apparatus according to claim 9, wherein said means for supplyingmolten thermoplastic material comprises a conduit communicating betweena supply of molten thermoplastic material and the internal faces of saidopposed edges.

References Cited UNITED STATES PATENTS 2,471,258 5/1949 Bolten 18-362,488,212 11/1'949 Lloyd. 3,081,213 3/1963 Chin.

BERNARD STICKNEY, Primary Examiner.

1. A METHOD OF CLOSING AN END OF A FLAT TUBE OF SHEET MATERIAL TO FORM ABAG THEREOF, SAID METHOD COMPRISING IN COMBINATION THE STEPS OF MOLDINGA BEAD OF THERMOPLASTIC MATERIAL ABOUT A PAIR OF JUXTAPOSED EDGES OF ANEND OF SAID FLAT TUBE, SAID BEAD EXTENDING AT LEAST FROM ONE SIDE TO THEOTHER SIDE OF SAID FLAT TUBE, AND HARDENING SAID THERMOPLASTIC MATERIAL.